Slipper type apex seal for rotary piston engine

ABSTRACT

A T-shaped apex seal for rotary piston engines, the upright of the T being pivotally mountable in an apex seal groove of the multilobed rotor and the cross bar of the T having trochoid rotor chamber surface engaging raised sealing ribs lengthwise thereof and spaced a substantial distance to either side of the center line of the upright, with the rib at the leading side of the cross bar being spaced a greater distance from the center line than the rib at the trailing side of the cross bar. Grooves are provided alongside the apex seal groove to receive the side portions of the cross bar as it tilts relative to the seal groove in the pivotal movements of the apex seal as it follows the rotor chamber surface in the rotation of the rotor.

United States Patent [191 1 Prasse et al.

vSUPPER TYPE APEX SEAL FOR ROTARY PISTON ENGINE lnventors: Herbert F Prasse, Town and Country; Harold E. McCormick, Ballwin; William F. Ott, St. Louis, all of Mo.

Assignee: Ramsey Corporation, St. Louis, Mo.

Filed: Oct. 1, 1971 Appl. No.: 185,582

US. Cl. 418/118, 418/117 Int. Cl. F0lc 19/04 Field of Search 418/118, 124, 113, 61, 418/114. 115, 116,117, 119, 120,121,122, 123

References Cited UNITED STATES PATENTS .872 9/1965 Pomasanow 418/122 X .013 i2/l965 Toxoda et al 4l8/ll6X Eickmann 418/61 Mar. 19, 1974 Primary Examiner-Carlton R. Croyle Assistant Examiner--Michael Koczo, Jr.

Attorney, Agent, or Firm-Hill, Sherman, Meroni. Gross & Simpson [57] TRACT A T-shaped apex seal for rotary piston engines, the upright of the T being pivotally mountable in an apex seal groove of the multilobed rotor and the cross bar of the T having trochoid rotor chamber surface engaging raised sealing ribs lengthwise thereof and spaced a substantial distance to either side of the center line of the upright. with the rib at the leading side of the cross bar being spaced a greater distance from the center line than the rib at the trailing side of the cross bar; Grooves are provided alongside the apex seal groove to receive the side portions of the cross bar as it tilts relative to the seal groove in the pivotal movements of the apex seal as it follows the rotor chamber surface in the rotation of the rotor.

10 Claims, 10 Drawing Figures SLHPPER TTWE APEX SEAL FOR ROTARY PISTON ENGINE BACKGROUND OF THE INVENTION 1. Field of the invention- This invention relates to internal combustion engines and more particularly to an apex seal for a rotary piston internal combustion engine.

. 2. Prior Art Rotary piston engines, particularly of the Wankel type, utilize multi-sided rotary pistons received in a variously configured chamber. The periphery of the rotor contains a number of apex points where adjacent sides of the periphery meet. These apex points are adapted to ride against the surface of the rotor chamber in sealing relation therewith thus dividing the chamber into a number of areas in which the simultaneous modes of intake, compression, power and exhaust, corresponding with the strokes of the four-stroke piston engine, occur.

in order to provide an effective seal at the apex between the rotor and the bore of the chamber, it has heretofore been known to provide grooves in the periphery of the rotor at the apex and to insert seal members in the grooves for spring urged contact against the bore of the chamber.

The axial ends of the chamber are closed by end plates. The prior art has found it mechanically difficult to provide adequate seals at the axial ends of the apex grooves. Inasmuch as the grooves contain an apex seal which is urged radially outwardly into contact with the bore of the chamber, it has been difficult to provide a seal member which can be urged axially outward into contact with the end plates. Theprior art has heretofore attempted to solve this problem through the provision of counterbores at the axial ends of the apex groove and the insertion therein of corner seals which can be spring backed to be urged axially while at the same time containing a groove to receive the ends of the apex seal. These counterbores have provided leakage paths.

Another problem encountered in connection with the prior art apex seals, has been the inability of the seal to move with respect to the groove in which it is received. Contact between the sealing face of the apex seal and the bore of the chamber changes in angularity as the rotor rotates through the bore.'These changes in the angularity of contact have heretofore been met through the provision of a curved surface apex vane seal. This has, however, greatly increased the wear of the seal, while at the same time keeping the sealing contact point at a minimum, thereby allowing through-- leakage. Additionally, the change in the angle at which the seal contacts the bore has. aggravated the heretofore encountered problem of excessive wear in the chamber caused by chatter between the vanes and the bore. Y

A third problem encountered with the prior art seals occurs from the fact that the spark plugs are introduced to the chamber in a counterbore in the bore surface of the chamber. This counterbore, of necessity, has an opening to the chamber. As the prior art vanes passed over the opening, leakage space was created through the counterbore from the leading to the trailing sides of the vane.

SU 1 OF THE INVENTION The above problems encountered in connection with the prior art apex seals are overcome by the present invention which utilizes an oscillating slipper for the seal. The rotor is modified to provide a circular or curved groove at the apex, the opening to the groove having a diameter less than the full diameter of the groove, in a preferred embodiment. Further, ledges are provided in the leading and trailing surfaces adjacent the groove. A slipper carrier member having a generally cylindrical shape is received in the groove, the carrier providing a groove for receipt of a portion of the slipper seal. In one embodiment the carrier is rotatable within the groove, whereas in another embodiment combination corner seal and compression seals as used with this invention provide an interlock to prevent rotation of the carrier.

The slipper seal is T-shaped in cross section having raised sealing ribs on the outer surface of the cross bar of the T. These ribs are adapted to contact the surface of the bore and are spaced from one another transverse of the cross bar. The upright of the T is received in the groove of the carrier. In the embodiment providing for rotation of the carrier, the upright is a straight upright which is rectangular in cross section and which is snugly received in the groove, allowing the carrier and slipper both to rotate with respect to the groove. In the other embodiment, the upright is bulb-shaped and is itself pivotal within the groove of a non-pivotal carrier.

The sealing ribs contact the bore of the rotor at spaced points which are dimensioned to span the distance of the counterbore of the spark plugs to prevent the opening of a leakage path thereacross. The ribs have a height dimension set to accommodate movement over the angled points of the trochoid chamber. The recesses in the surface of the rotor receive either the. leading or trailing portions of the slipper when it is at its greatest points of angulation with respect to the apex groove.

In the preferred embodiment the rib on the trailing side of the cross piece is spaced from the trailing edge of the cross piece and is located closer to the center line of the upright of the slipper seal than the rib at the leading side of the cross piece which is spaced farther from the center line than the trailing rib.

Because the seal oscillates in the groove, the contact between the sealing ribs and the surface of the bore is more nearly optimized for all positions of the rotor in the bore therebyv eliminating the change in angularity of sealing contact. Thus, a reduction in the amount of chatter between the seal and bore is attained. Additionally, due to the provision of wishbone-type combined corner and compression seals, the heretofore existing leakage path at the corner seals is eliminated.

It is therefore an object of this invention to provide an improved apex seal for rotary piston engines.

It is a further object'of this invention to provide a slipper type apex seal for use in rotary piston engines.

It is another and more specific object of this invention to provide a T-shaped cross section slipper seal for use in sealing the apexes of rotary pistons in rotary piston engines.

It is another object of this invention to provide an oscillating apex seal for rotary piston engines.

It is a general object of this invention to provide an improved apex seal for rotary pistonengines which reduces heretofore encountered sealing and wear problems.

Other objects, advantages and capabilities of the in vention will become apparent-from the following description taken in conjunction with the accompanying drawings showing preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective exploded view of a rotor equipped with the apex seals of this invention;

FIG. 2 is a plan view of a partially disassembled rotor chamber equipped with a rotorhaving apex seals;

FIG. 3 is an end plan view of an apex seal according to this invention;

FIG. 4 is a view similar to FIG. 3 illustrating a modified apex seal according to thisinvention;

FIG. 5 is a top plan view of an apex seal according to this invention;

FIG. 6 is a fragmentary perspective exploded view of a rotor equipped with the apex seal of FIG. 4 of this invention;

FIG. 7 is a fragmentary view illustrating the positioning of a rotor equipped with the slipper seal of this invention in the rotor chamber; and

FIGS. 8, 9 and 10 are fragmentary views of the apex seal. rotor bore contact area illustrating the pivotability of the apex seals of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a rotary piston engine rotor 10 of a groove for the vane 32, as compared to the contact made by the vane 31.

As the rotor 10b rotatesin the bore 33, the contact point for each of the vanes is continuously changing with respect to the angularity of contact. This contributes to vane chatter against the surface of the bore 33 which increases the wear rate of both the vane and the bore while at the same time opening momentary leakage paths between the surface of the bore and the surface of the vane.

FIGS. 3, 4 and 5 illustrate the slipper-type seals 37 and 380i our invention. The seals are basically T- shaped in cross section comprising an upright member 39 and a cross bar member 40 positioned at the top of the upright member 39 and at right angles thereto.

The cross bar members 40 have a pair of lengthwise extending raised sealing ribs 41 thereon which may have lengthwise extending grooves 42 therein which can be filled with a hard wear-resistant coating 43. The outer surfaces of the ribs 41 provide the sealing surfaces between the seals 37 and 38 and the bore of the rotor chamber. One of the ribs 41a is placed at the leading edge 45 of the cross bar 40. The other of the ribs 41b is placed adjacent to, but spaced from, the

trailing edge 46 of the cross member. Thus, the trailing edge rib 41b is spaced in toward the upright 39 from the trailing edge 46 and the ribs 41a and 41b are spaced from one another transverse of the cross bar at unequal distances from the centerline of the upright wherein the. rib 41a on the leading side portion of the cross baris spaced a greater distance from the centerline of theupright than the rib 41b on the trailing side standard type. The rotor has three outer peripheral sides l1, l2 and 13. The points of contact between the sides occurs at a line across the periphery calledan apex 14, 15 and 16. The axial end walls 17 and 18 are provided with compression seal grooves 19 and the apexes are provided with apex seal grooves 20. As is common, the compression seal grooves 19 are positioned near the periphery of the rotor and the longitudinal ends of the compression grooves terminate at the apex grooves and are open thereto.

The compression seals 21 used with the illustrated embodiments. ofthe apex seal of this invention consists of wishbone-shaped members having centralhubs 22 which are dimensioned to be received in the axial ends of the apex grooves and from which depend compres sion seal legs 23 which are received in the grooves 19. Since the hubs 22 and legs 23 are integral, no leakage path canopen therebetween. FIG. 2 illustrates a rotor 10b equipped with vane type apex seals 30, 31 and 32.

in the trochoid bore 33 of a rotary piston engine 34. The vane-type The rotor as illustrated, is received apex seals 30, 31 and 32 are not pivotal in the apex grooves of the rotor 10!). FIG. 2 illustrates the changing angularity of contact between the apex seals and the bore 33. As can be seen, the vane30, which portion of the cross bar is spaced from the centerline of the upright.

As illustrated in FIG. 5, the ribs 41a and 41b extend lengthwise of the cross member 40 for the entire length thereof and are spaced apart transverse of the cross bar 40. In the preferred embodiment the distance by which the ribs 410 and 41b are spaced apart transversely corresponds to the width of the opening for the spark plugs in the bore of the chamber. Thus. as the slipper seal passes the opening to the spark plug, a point will occur when the entire opening is straddled by the slipper with the leading edge rib 41a on one side of the opening and a trailing edge rib 41b on the other side, thereby preventing a leakage path from opening through the spark plug opening.

It will be appreciated that in certain embodiments the spacing of theribs can be less than the opening for the spark plugs without eliminating the reduction in leakage path which results from the use of spaced apart ribs.

The height to which the ribs 41a and 41b project above the surface of the cross bar 40, is a function of the distance by which they are spaced apart transversely and the sharpness of the nodal points. or curve intersections of the chamber bore. The flatter the curve intersection points, the less the height of the ribs. The ribs must have a height sufficient so that when the ribs are equidistantly spaced from the line of curve intersection or nodal point of the bore, one rib on either side of the line, there will be no contact between the bore and the surface of the cross bar 40 except for contact between the ribs and the bore surface.

In order to allow for continuous contact between the outer surfaces of the ribs and the bore, throughout the 360 rotation of the rotor. the apex seals of this invention are pivoted within the apex grooves. Thus, the apex seals of this invention can be described as swinging slipper seals.

In order to provide for the pivotability of the upright member 39 of the seals with respect to the apex grooves, while at the same time minimizing the opening of any leakage path through the grooves from the leading to trailing sides of the seal, a seal carrier 500 or 50b is provided in the groove 20. In one embodiment the carrier 50a is prevented from pivoting in the groove and the slipper seal 37 is allowed to pivot in the carrier. In another embodiment, the carrier 50b is allowed to pivot in the apex groove 20 and the apex seal 38 is prevented from pivoting in the carrier. It will be appreciated in either embodiment that the slipper seal pivots with respect to the apex seal groove 20.

A non-pivoting carrier embodiment is illustrated in FIG. 1 and utilizes the slipper seal of FIG. 3. The apex groove 20 is preferably circular as illustrated M52 and has a groove opening 53 having a width less than the diameter of the groove. The apex carrier 50a is tubular having a seal receiving groove 56 therein lengthwise thereof. The carrier 50a has a diameter approximately equal to the diameter of the groove 20 and is received therein in snug relation, thereby preventing the opening of any leakage path through the groove 20 between the surface of the groove and the surface of the carrier. The carrier 5011 has reduced diameter bores 57 extend ing into the axial ends of the carrier with notched openings 58 through the periphery of the reduced diameter bore. The hubs 22 of the combination corner and compression seal members 21 have reduced diameter tubular projections 60 at their inner axial ends 61 which project into the grooves 20. The reduced diameter projections 60 are dimensioned to be snugly received in the reduced diameter bores 57 of the carriers 50a. Projecting nibs 62 extend outwardly from the reduced diameterprojection 60 at spaced apart points dimensioned to be received in the notches 58. In this way the carrier 50a is locked against rotation with respect to the hubs 22 of the combination comer and compression seal members 21. Since one hub 22 projects into each axial end of the carrier 50a, the carrier is locked against rotation in the groove 20. The hubs 22 have grooves 65 opening therein which are codimensioned with the grooves 56 in the carrier and aligned therewith providing a continuous groove across the apex of the rotor for receipt of the upright of the slipper seal 87. The upright of the seal 47, best illustrated in FIG. 3, is shaped in the manner ofa bulb having a cylindrical base portion 70 which is attached to the cross bar 40 through a narrow waist portion 71. The circular portion 70 is received in the grooves 56, 65 with a line contact between the outer surface of the bulb and the side and bottom walls of the groove this contact surface is continuous throughout the pivoting of the seal in the groove 56, 65, thereby sealing the groove against leakage between the side walls of the groove and the surface of the upright of the slipper seal 37. However, because the surface of the bulb 70 is not planar. the bulb is able to pivot in the groove 56, 65.

It is. of course. to be understood that with respect to the embodiment just described that the groove 20 in the rotor could be other than circular and that mating planar faces could exist between the groove 20 and the carrier 50a inasmuch as the carrier 500 does not pivot in the groove 20. It is further to be understood that the combined groove 56, is illustrated as being rectangular in cross section because such a configuration minimizes frictional contact area between the circular surface of the bulb and the walls of the groove. However. the combined groove 56, 65 could have a different configuration, such as by way of example. circular. to mate with the bulb 70. It is further to be understood that the upright 39 of the seal 37 can have a configuration other than that illustrated, the illustration merely showing one method of providing for a pivoting seal which can pivot in a non-pivoting carrier without opening a leakage path between the upright of the slipper seal and the groove in which it is received.

In an alternative embodiment, best illustrated in FIG. 6, the carrier 50b is allowed to rotate in the groove 20b of the rotor while the upright 70b of the slipper seal 38 is prevented from rotating in the groove 56b of the carrier.

In the embodiment illustrated in FIG. 6, the carrier 50b has reduced diameter projections and 81 at the axial ends of a cylindrical carrier. The reduced diameter projections are received in cylindrical openings 83 in the hubs 22b of the combination corner and compression seal members. The hubs 2212 have a wide groove opening 82 open to the openings 31. The climensioning of the opening 82 is determined with respect to the amount of pivotability of the carrier 5%. The groove 56b of the carrier 59b extends from one axial end to the other axial end and is dimensioned to snugly receive the upright 70b of the slipper apex seal 38. In the embodiment illustrated, the groove 56b has planar side walls 84 and 85 and a planar bottom wall providing a rectangular cross section opening and the upright 70b of the slipper seal is rectangular having planar side walls 86 and 87 to mate against the walls 84 and 85, thereby preventing pivoting of the upright 70b in the groove 56b. However, because the carrier 50b is cylindrical and the groove 20b is circular, the carrier 50b is pivotable within the groove 20b, thereby allowing pivotability of the slipper seal 38 with respect to the groove 20b. Further, because the reduced diameter projections 80 and $1 are cylindrical and the openings 81 in the hubs 22b are circular, the carrier 56b is pivotable or rotatable in the hubs 2212. When assembled the groove 56b aligns with the opening'82 in the hubs.

It will, of course. be understood that in the embodiment illustrated in FIG. 6, the configuration of the groove 20b and of the opening 81 can be different than that illustrated. so long as the carrier 50b is pivotable in the groove and the hubs.

FIGS. 7 through 10 illustrate the pivoting of the slipper seal with respect to the rotor apex groove as the seal moves around the bore surface of the rotor chamber.

FIG. 7 illustrates a rotor 91- received within the sur- 7 face 92 of a chamber. The Figure illustrates placement of the seals 93 and 94 at the apexes andillustrates that the contact between the surface of the bore 92 and the apex seals is at the ribs 41 with clearance between the surface 92 and the surface of the cross bar 40. If it is assumed that the rotor is rotating in the chamber in the direction of the arrow and that the apex seal 93a is the seal illustrated in FIGS. 8, 9 and 10, the FIG. 8 illustrates the seal 93 as it approaches a curve intersection line or nodal point 95. At such a position, the leading edge 97 of the seal 93 is closer, to the periphery 98 of the rotor than is the trailing edge 99, and the seal 93 is pivoted in the groove 100 towards the leading edge of the groove. FlG.9 illustrates the seal 93 as it passes over the nodal point 95. At that point the seal is not angled with respect to the groove and the upright 39 extends perpendicularly out of the groove 100. As the seal 93 passes the nodal point, as illustrated in FIG. 10,

the seal pivots in the groove 100 towards the trailing edge of the groove so that the trailing edge 99 of the seal 93 is closer to the surface 98 of the rotor thamis the leading edge 97.

In order to minimize the amount of projection of the cross member 40 above the apex of the rotor, the rotor is recessed adjacent the leading and trailing edges of the apex groove as best illustrated in FIG. 6. The recesses 101, 102 provide seats for the leading and trailing portions of the cross bar 40 so that as the apex seal pivots in the grooves, the leading or trailing portions of the cross member can dip into and out of the recesses 101, 102. This allows for the provision of a maximum size rotor in the chamber without interferring with the curvature of the rotor periphery.

It therefore will be appreciated that our invention provides a slipper-type apex seal for rotary piston engines, the seal. being T-shaped in cross section providing a cross bar having length and width dimensions, the

length corresponding to the distance between the end plates. A pair of raised ribs extend the length of the cross member and are positioned on the outer surface thereof and are spaced from one another transverse of the cross member. The ribs provide asealing surface for the slipper seal and are adapted to engage and ride against the bore of the rotor chamber. The slipper seal is pivotable with respect to the rotor to accommodate the non-circular bore surface. We have herein described our invention in two embodiments, one of which allows the slipper seal to be received in a carrier which in turn is received in the apex groove of the ro-, tor, the slipper being non-pivotably received in the carrier and the carrier pivotably received in the rotor. In another embodiment, the slipper is pivotably received in a carrier which is non-pivotably received in the apex groove of the rotor.

Although the teachings of our invention have herein been discussed with reference to specific theories and embodiments and although illustrative means for accomplishing explained results have been described, it is to be understood that these are by way of illustration only and that others may wish to utilize our invention in different designs or applications.

We claim as our invention:

1. in a rotary piston internal combustion engine having a multi-sided outer periphery rotor, the sides meeting at apex lines and seals provided at the apex lines, the improvement Of said seals being slipper seals having an upright section topped by a cross bar projecting at substantially right angles to the upright, the cross bar having on its outside surface at least two projecting ribs extending lengthwise of the cross bar, the said ribs spaced from one another transverse of the cross bar at unequal distances from the centerline of the upright, the said upright pivotably received in an apex line. groove in the rotor.

2. A seal member for use as the apex sealin a rotary piston engine, the seal comprising a member having .a first surface with a centerline, two spaced-apart parallel raised contact surfaces projecting from the first surface extending parallel to the centerline, the contact surfaces being unequally spaced from the centerline whereby one contact surface is spaced closer to the centerline than a second contact surface.

3. seal member of claim 2 wherein the seal member is a substantially T-shaped cross section member having an upright connected to a cross bar, the first surface lying on an outer surface of the cross bar, the upright received :in a seal carrier, and the seal carrier received in a groove in a rotary piston, the groove lying along an apex ,of the piston.

4. In a rotary piston engine having a multi-sided outer periphery rotor received in a rotor chamber with a spark plug opening through a chamber wall Opposite the outer periphery of the rotor, the spark plug opening having a diameter at the wall, the sides of the rotor meeting ,at apex lines and seals provided at the apex lines, the improvement comprising:

said seals being slipper seals each having a surface thereon oppositethe chamber wall; the surface having at least two projecting ribs extending lengthwise the entire length of the surface;

the ribs projecting from the surface and being spaced from one another transverse of the surface by a distance greater than the diameter of the spark plug opening;

said seals each having means pivotally mounting the same at the apex line and each of the seals being provided with a leading portion at one side of the .pivot means and a trailing portion at the opposite side of the pivot means;

one of said ribs being on .said leading portion and being spaced a greater distance from said pivot means than the other of the ribs which is on the trailing portion and is spaced a lesser distance from said pivot means than said n'b on the leading side portion of the seal. 1

5. An apex seal for a rotary piston received in a rotor housing, the rotor housing having a spark plug aperture therethrough, the seal comprising a swinging slipper seal member pivotably received in an apex groove and having an axis of rotation in said groove, the said groove lying at an apex of the rotor, the seal member having at least two raised contact surfaces thereon between the seal and the rotor housing, the said contact surfaces being unequally spaced from a first plane which passes through the axis rotation of the said seal, the said contact surfaces being substantially parallel and spacedfrorn the first plane in a plane normal to the first plane. Y

6. The seal of claim 5 in which the distance between the seal contact surfaces isequal to or larger than the spark plug opening.

7. In a rotary piston internal combustion engine having a multi-sided outer diameter periphery rotor for running along a trochoid chamber wall, the sides meeting at apex lines and having grooves along ,the apex lines:

slipper seals each having ,an upright portion topped by cross bar projecting at Substantially right angles to the upright portion and providing a leading side portion and a trailing side portion;

said cross bar having a chamber wall engaging surface provided with a pair of spaced parallel chamber wall engaging ribs extending throughout the length of the cross bar, one of said ribs being on 8. The improvement of claim I, wherein one of the said ribs is positioned adjacent the leading edge of the said cross bar and the other of said ribs is positioned adjacent to and spaced from the trailing edge of the said cross bar.

9. The improvement of claim 8, wherein the said upright is rectangular in cross section.

10. The improvement of claim 8, wherein the said upright has a curved surface portion.

'1 t i fl i 

1. In a rotary piston internal combustion engine having a multisided outer periphery rotor, the sides meeting at apex lines and seals provided at the apex lines, the improvement Of said seals being slipper seals having an upright section topped by a cross bar projecting at substantially right angles to the upright, the cross bar having on its outside surface at least two projecting ribs extending lengthwise of the cross bar, the said ribs spaced from one another transverse of the cross bar at unequal distances from the centerline of the upright, the said upright pivotably received in an apex line groove in the rotor.
 2. A seal member for use as the apex seal in a rotary piston engine, the seal comprising a member having a first surface with a centerline, two spaced-apart parallel raised contact surfaces projecting from the first surface extending parallel to the centerline, the contact surfaces being unequally spaced from the centerline whereby one contact surface is spaced closer to the centerline than a second contact surface.
 3. The seal member of claim 2 wherein the seal member is a substantially T-shaped cross section member having an upright connected to a cross bar, the first surface lying on an outer surface of the cross bar, the upright received in a seal carrier, and the seal carrier received in a groove in a rotary piston, the groove lying along an apex of the piston.
 4. In a rotary piston engine having a multi-sided outer periphery rotor received in a rotor chamber with a spark plug opening through a chamber wall Opposite the outer periphery of the rotor, the spark plug opening having a diameter at the wall, the sides of the rotor meeting at apex lines and seals provided at the apex lines, the improvement comprising: said seals being slipper seals each having a surface thereon opposite the chamber wall; the surface having at least two projecting ribs extending lengthwise the entire length of the surface; the ribs projecting from the surface and being spaced from one another transverse of the surface by a distance greater than the diameter of the spark plug opening; said seals each having means pivotally mounting the same at the apex line and each of the seals being provided with a leading portion at one side of the pivot means and a trailing portion at the opposite side of the pivot means; one of said ribs being on said leading portion and being spaced a greater distance from said pivot means than the other of the ribs which is on the trailing portion and is spaced a lesser distance from said pivot means than said rib on the leading side portion of the seal.
 5. An apex seal for a rotary piston received in a rotor housing, the rotor housing having a spark plug aperture therethrough, the seal comprising a swinging slipper seal member pivotably received in an apex groove and having an axis of rotation in said groove, the said groove lying at an apex of the rotor, the seal member having at least two raised contact surfaces thereon between the seal and the rotor housing, the said contact surfaces being unequally spaced from a first plane which passes through the axis rotation of the said seal, the said contact surfaces being substantially parallel and spaced from the first plane in a plane normal to the first plane.
 6. The seal of claim 5 in which the distance between the seal contact surfaces is equal to or larger than the spark plug opening.
 7. In a rotary piston internal combustion engine having a multi-sided outer diameter periPhery rotor for running along a trochoid chamber wall, the sides meeting at apex lines and having grooves along the apex lines: slipper seals each having an upright portion topped by cross bar projecting at Substantially right angles to the upright portion and providing a leading side portion and a trailing side portion; said cross bar having a chamber wall engaging surface provided with a pair of spaced parallel chamber wall engaging ribs extending throughout the length of the cross bar, one of said ribs being on the leading side portion of the cross bar and spaced from the centerline of said upright portion and the other of said ribs being on the trailing side portion of the cross bar and spaced from said centerline of the upright portion; said uprights of the seals being received in respective ones of said apex line grooves in the rotor; means accommodating pivoting of said cross bars in their grooves and with respect to the rotor; and recesses along said grooves to receive said cross bar side portions in the pivoting of the seals.
 8. The improvement of claim 7, wherein one of the said ribs is positioned adjacent the leading edge of the said cross bar and the other of said ribs is positioned adjacent to and spaced from the trailing edge of the said cross bar.
 9. The improvement of claim 8, wherein the said upright is rectangular in cross section.
 10. The improvement of claim 8, wherein the said upright has a curved surface portion. 